1. Field of the Invention
The present invention relates to selected liquid, radiation-curable compositions which are particularly suitable for the production of three-dimensional articles by stereolithography as well as a process for the production of cured articles and the cured three-dimensional shaped article themselves. In particular, this invention relates to liquid, radiation-curable resin compositions from which cured three-dimensional shaped articles having both high temperature resistance and high impact resistance can be made.
2. Brief Description of Art
The production of three-dimensional articles of complex shape by means of stereolithography has been known for a relatively long time. In this technique the desired shaped article is built up from a liquid, radiation-curable composition with the aid of a recurring, alternating sequence of two steps (a) and (b); in step (a), a layer of the liquid, radiation-curable composition, one boundary of which is the surface of the composition, is cured with the aid of appropriate radiation, generally radiation produced by a preferably computer-controlled laser source, within a surface region which corresponds to the desired cross-sectional area of the shaped article to be formed, at the height of this layer, and in step (b) the cured layer is covered with a new layer of the liquid, radiation-curable composition, and the sequence of steps (a) and (b) is repeated until a so-called green model of the desired three-dimensional shape is finished. This green model is, in general, not yet fully cured and must therefore, normally, be subjected to post-curing.
The mechanical strength of the green model (modulus of elasticity, fracture strength), also referred to as green strength, constitutes an important property of the green model and is determined essentially by the nature of the stereolithographic-resin composition employed. Other important properties of a stereolithographic resin composition include a high sensitivity for the radiation employed in the course of curing and a minimum curl factor, permitting high shape definition of the green model. In addition, for example, the precured material layers should be readily wettable by the liquid stereolithographic resin composition, and of course not only the green model but also the ultimately cured shaped article should have optimum mechanical properties.
Another requirement that has recently become a high priority for stereolithography users is the high temperature performance of cured articles produced by stereolithography. It is usually measured by the Heat Deflection Temperature (HDT) or Glass Transition Temperature (Tg). The HDT value is determined by the ASTM method D648 applying a load of 66 psi.
In order to achieve the desired balance of properties, different types of resin systems have been proposed. For example, radical-curable resin systems have been proposed. These systems generally consist of one or more (meth)acrylate compounds (or other free-radical polymerizable organic compounds) along with a free-radical photoinitiator for radical generation. U.S. Pat. No. 5,418,112 describes one such radical-curable system.
Another type of resin composition suitable for this purpose is a dual type system that comprises (i) epoxy resins or other types of cationic polymerizable compounds; (ii) cationic polymerization initiator; (iii) acrylate resins or other types of free radical polymerizable compounds; and (iv) a free radical polymerization initiator. Examples of such dual or hybrid systems are described in U.S. Pat. No. 5,434,196.
A third type of resin composition useful for this application also includes (v) reactive hydroxyl compounds such as polyether-polyols. Examples of such hybrid systems are described in U.S. Pat. No. 5,972,563.
Despite all previous attempts, there exists a need for a liquid hybrid stereolithographic composition capable of producing cured articles that possesses both high temperature resistance and high impact resistance. The present invention presents a solution to that need.